The present invention relates to a divided function type electrophotographic sensitive member formed of amorphous silicon and amorphous silicon carbide, in particular to an electrophotographic sensitive member capable of widening particularly an optical band gap range to heighten an optical sensitivity.
Recently, the development of a super high speed copying machine, a laser beam printer and the like has actively progressed. Stabilized operation characteristics and durability have been required for an electrophotographic sensitive drum carried on such instruments with this development. As for these requirements, hydrogenized amorphous silicon is being watched with interest from the viewpoints of superior abrasion resistance, heat resistance, antipollution property, optical sensitive characteristics and the like.
A multi-layer type sensitive member shown in FIG. 3 has been proposed for an electrophotographic sensitive member formed of such amorphous silicon (hereinafter referred to as a-Si).
That is to say, referring to FIG. 3, an a-Si carrier barrier layer (2a), an a-Si carrier-generating layer (3a) and a surface-protecting layer (4a) are piled up in turn on an electrically conductive substrate (1a) such as aluminum, said carrier barrier layer (2a) being formed for preventing carriers from being injected from said substrate (1a) and lowering a residual potential, and said surface-protecting layer (4a) being formed of materials of high hardness to heighten the durability of the sensitive member.
However, with this a-Si sensitive member, a dark resistance of the a-Si carrier-generating layer (3a) itself is 10.sup.11 .OMEGA..multidot.cm or less, so that a darkness-attenuation speed of this sensitive member is increased and it is difficult to heighten a charge-acceptance of this sensitive member itself, whereby problems occur in that in the event that this sensitive member is used in the high-speed copying, the preceding image remains without being completely removed by an optical memory effect and appears again with the formation of the subsequent image (this is referred to as a residual image in the present invention).
In order to solve these problems, a divided function type sensitive member shown in FIG. 4 has been proposed.
That is to say, referring to FIG. 4, a carrier transport layer (5a) and a carrier-generating layer (3b), and a surface protective layer (4a) if necessary, are formed in turn on an electrically conductive substrate (1a) to obtain a multi-layer type sensitive member. Said carrier transport layer (5a) is formed of materials capable of increasing both the dark resistance and the carrier mobility. And, with a divided function type sensitive member, in which the above described respective layers are formed of a-Si or amorphous silicon carbide (hereinafter referred to as a-SiC) obtained by doping a-Si with carbon atoms (C), even though it was used in the high-speed copying, said residual image could be prevented from occurring.
However, in the case where the above described sensitive member is used in the high-speed copying in the above described manner, the problems occur in that the image exposure perone time of copying is reduced by the high-speediness, so that the sufficient optical attenuation is not obtained and the potentiality of the sensitive member corresponding to the shading contrast of the manuscript is not sufficiently increased, whereby the background smearing is produced.